diff options
Diffstat (limited to 'nsprpub/pr/src/threads/prcmon.c')
| -rw-r--r-- | nsprpub/pr/src/threads/prcmon.c | 431 |
1 files changed, 431 insertions, 0 deletions
diff --git a/nsprpub/pr/src/threads/prcmon.c b/nsprpub/pr/src/threads/prcmon.c new file mode 100644 index 000000000..2a196e9d4 --- /dev/null +++ b/nsprpub/pr/src/threads/prcmon.c @@ -0,0 +1,431 @@ +/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +#include "primpl.h" + +#include <stdlib.h> +#include <stddef.h> + +/* Lock used to lock the monitor cache */ +#ifdef _PR_NO_PREEMPT +#define _PR_NEW_LOCK_MCACHE() +#define _PR_DESTROY_LOCK_MCACHE() +#define _PR_LOCK_MCACHE() +#define _PR_UNLOCK_MCACHE() +#else +#ifdef _PR_LOCAL_THREADS_ONLY +#define _PR_NEW_LOCK_MCACHE() +#define _PR_DESTROY_LOCK_MCACHE() +#define _PR_LOCK_MCACHE() { PRIntn _is; _PR_INTSOFF(_is) +#define _PR_UNLOCK_MCACHE() _PR_INTSON(_is); } +#else +PRLock *_pr_mcacheLock; +#define _PR_NEW_LOCK_MCACHE() (_pr_mcacheLock = PR_NewLock()) +#define _PR_DESTROY_LOCK_MCACHE() \ + PR_BEGIN_MACRO \ + if (_pr_mcacheLock) { \ + PR_DestroyLock(_pr_mcacheLock); \ + _pr_mcacheLock = NULL; \ + } \ + PR_END_MACRO +#define _PR_LOCK_MCACHE() PR_Lock(_pr_mcacheLock) +#define _PR_UNLOCK_MCACHE() PR_Unlock(_pr_mcacheLock) +#endif +#endif + +/************************************************************************/ + +typedef struct MonitorCacheEntryStr MonitorCacheEntry; + +struct MonitorCacheEntryStr { + MonitorCacheEntry* next; + void* address; + PRMonitor* mon; + long cacheEntryCount; +}; + +/* +** An array of MonitorCacheEntry's, plus a pointer to link these +** arrays together. +*/ + +typedef struct MonitorCacheEntryBlockStr MonitorCacheEntryBlock; + +struct MonitorCacheEntryBlockStr { + MonitorCacheEntryBlock* next; + MonitorCacheEntry entries[1]; +}; + +static PRUint32 hash_mask; +static PRUintn num_hash_buckets; +static PRUintn num_hash_buckets_log2; +static MonitorCacheEntry **hash_buckets; +static MonitorCacheEntry *free_entries; +static PRUintn num_free_entries; +static PRBool expanding; +static MonitorCacheEntryBlock *mcache_blocks; + +static void (*OnMonitorRecycle)(void *address); + +#define HASH(address) \ + ((PRUint32) ( ((PRUptrdiff)(address) >> 2) ^ \ + ((PRUptrdiff)(address) >> 10) ) \ + & hash_mask) + +/* +** Expand the monitor cache. This grows the hash buckets and allocates a +** new chunk of cache entries and throws them on the free list. We keep +** as many hash buckets as there are entries. +** +** Because we call malloc and malloc may need the monitor cache, we must +** ensure that there are several free monitor cache entries available for +** malloc to get. FREE_THRESHOLD is used to prevent monitor cache +** starvation during monitor cache expansion. +*/ + +#define FREE_THRESHOLD 5 + +static PRStatus ExpandMonitorCache(PRUintn new_size_log2) +{ + MonitorCacheEntry **old_hash_buckets, *p; + PRUintn i, entries, old_num_hash_buckets, added; + MonitorCacheEntry **new_hash_buckets; + MonitorCacheEntryBlock *new_block; + + entries = 1L << new_size_log2; + + /* + ** Expand the monitor-cache-entry free list + */ + new_block = (MonitorCacheEntryBlock*) + PR_CALLOC(sizeof(MonitorCacheEntryBlock) + + (entries - 1) * sizeof(MonitorCacheEntry)); + if (NULL == new_block) return PR_FAILURE; + + /* + ** Allocate system monitors for the new monitor cache entries. If we + ** run out of system monitors, break out of the loop. + */ + for (i = 0, p = new_block->entries; i < entries; i++, p++) { + p->mon = PR_NewMonitor(); + if (!p->mon) + break; + } + added = i; + if (added != entries) { + MonitorCacheEntryBlock *realloc_block; + + if (added == 0) { + /* Totally out of system monitors. Lossage abounds */ + PR_DELETE(new_block); + return PR_FAILURE; + } + + /* + ** We were able to allocate some of the system monitors. Use + ** realloc to shrink down the new_block memory. If that fails, + ** carry on with the too-large new_block. + */ + realloc_block = (MonitorCacheEntryBlock*) + PR_REALLOC(new_block, sizeof(MonitorCacheEntryBlock) + + (added - 1) * sizeof(MonitorCacheEntry)); + if (realloc_block) + new_block = realloc_block; + } + + /* + ** Now that we have allocated all of the system monitors, build up + ** the new free list. We can just update the free_list because we own + ** the mcache-lock and we aren't calling anyone who might want to use + ** it. + */ + for (i = 0, p = new_block->entries; i < added - 1; i++, p++) + p->next = p + 1; + p->next = free_entries; + free_entries = new_block->entries; + num_free_entries += added; + new_block->next = mcache_blocks; + mcache_blocks = new_block; + + /* Try to expand the hash table */ + new_hash_buckets = (MonitorCacheEntry**) + PR_CALLOC(entries * sizeof(MonitorCacheEntry*)); + if (NULL == new_hash_buckets) { + /* + ** Partial lossage. In this situation we don't get any more hash + ** buckets, which just means that the table lookups will take + ** longer. This is bad, but not fatal + */ + PR_LOG(_pr_cmon_lm, PR_LOG_WARNING, + ("unable to grow monitor cache hash buckets")); + return PR_SUCCESS; + } + + /* + ** Compute new hash mask value. This value is used to mask an address + ** until it's bits are in the right spot for indexing into the hash + ** table. + */ + hash_mask = entries - 1; + + /* + ** Expand the hash table. We have to rehash everything in the old + ** table into the new table. + */ + old_hash_buckets = hash_buckets; + old_num_hash_buckets = num_hash_buckets; + for (i = 0; i < old_num_hash_buckets; i++) { + p = old_hash_buckets[i]; + while (p) { + MonitorCacheEntry *next = p->next; + + /* Hash based on new table size, and then put p in the new table */ + PRUintn hash = HASH(p->address); + p->next = new_hash_buckets[hash]; + new_hash_buckets[hash] = p; + + p = next; + } + } + + /* + ** Switch over to new hash table and THEN call free of the old + ** table. Since free might re-enter _pr_mcache_lock, things would + ** break terribly if it used the old hash table. + */ + hash_buckets = new_hash_buckets; + num_hash_buckets = entries; + num_hash_buckets_log2 = new_size_log2; + PR_DELETE(old_hash_buckets); + + PR_LOG(_pr_cmon_lm, PR_LOG_NOTICE, + ("expanded monitor cache to %d (buckets %d)", + num_free_entries, entries)); + + return PR_SUCCESS; +} /* ExpandMonitorCache */ + +/* +** Lookup a monitor cache entry by address. Return a pointer to the +** pointer to the monitor cache entry on success, null on failure. +*/ +static MonitorCacheEntry **LookupMonitorCacheEntry(void *address) +{ + PRUintn hash; + MonitorCacheEntry **pp, *p; + + hash = HASH(address); + pp = hash_buckets + hash; + while ((p = *pp) != 0) { + if (p->address == address) { + if (p->cacheEntryCount > 0) + return pp; + return NULL; + } + pp = &p->next; + } + return NULL; +} + +/* +** Try to create a new cached monitor. If it's already in the cache, +** great - return it. Otherwise get a new free cache entry and set it +** up. If the cache free space is getting low, expand the cache. +*/ +static PRMonitor *CreateMonitor(void *address) +{ + PRUintn hash; + MonitorCacheEntry **pp, *p; + + hash = HASH(address); + pp = hash_buckets + hash; + while ((p = *pp) != 0) { + if (p->address == address) goto gotit; + + pp = &p->next; + } + + /* Expand the monitor cache if we have run out of free slots in the table */ + if (num_free_entries < FREE_THRESHOLD) { + /* Expand monitor cache */ + + /* + ** This function is called with the lock held. So what's the 'expanding' + ** boolean all about? Seems a bit redundant. + */ + if (!expanding) { + PRStatus rv; + + expanding = PR_TRUE; + rv = ExpandMonitorCache(num_hash_buckets_log2 + 1); + expanding = PR_FALSE; + if (PR_FAILURE == rv) return NULL; + + /* redo the hash because it'll be different now */ + hash = HASH(address); + } else { + /* + ** We are in process of expanding and we need a cache + ** monitor. Make sure we have enough! + */ + PR_ASSERT(num_free_entries > 0); + } + } + + /* Make a new monitor */ + p = free_entries; + free_entries = p->next; + num_free_entries--; + if (OnMonitorRecycle && p->address) + OnMonitorRecycle(p->address); + p->address = address; + p->next = hash_buckets[hash]; + hash_buckets[hash] = p; + PR_ASSERT(p->cacheEntryCount == 0); + + gotit: + p->cacheEntryCount++; + return p->mon; +} + +/* +** Initialize the monitor cache +*/ +void _PR_InitCMon(void) +{ + _PR_NEW_LOCK_MCACHE(); + ExpandMonitorCache(3); +} + +/* +** Destroy the monitor cache +*/ +void _PR_CleanupCMon(void) +{ + _PR_DESTROY_LOCK_MCACHE(); + + while (free_entries) { + PR_DestroyMonitor(free_entries->mon); + free_entries = free_entries->next; + } + num_free_entries = 0; + + while (mcache_blocks) { + MonitorCacheEntryBlock *block; + + block = mcache_blocks; + mcache_blocks = block->next; + PR_DELETE(block); + } + + PR_DELETE(hash_buckets); + hash_mask = 0; + num_hash_buckets = 0; + num_hash_buckets_log2 = 0; + + expanding = PR_FALSE; + OnMonitorRecycle = NULL; +} + +/* +** Create monitor for address. Don't enter the monitor while we have the +** mcache locked because we might block! +*/ +PR_IMPLEMENT(PRMonitor*) PR_CEnterMonitor(void *address) +{ + PRMonitor *mon; + + if (!_pr_initialized) _PR_ImplicitInitialization(); + + _PR_LOCK_MCACHE(); + mon = CreateMonitor(address); + _PR_UNLOCK_MCACHE(); + + if (!mon) return NULL; + + PR_EnterMonitor(mon); + return mon; +} + +PR_IMPLEMENT(PRStatus) PR_CExitMonitor(void *address) +{ + MonitorCacheEntry **pp, *p; + PRStatus status = PR_SUCCESS; + + _PR_LOCK_MCACHE(); + pp = LookupMonitorCacheEntry(address); + if (pp != NULL) { + p = *pp; + if (--p->cacheEntryCount == 0) { + /* + ** Nobody is using the system monitor. Put it on the cached free + ** list. We are safe from somebody trying to use it because we + ** have the mcache locked. + */ + p->address = 0; /* defensive move */ + *pp = p->next; /* unlink from hash_buckets */ + p->next = free_entries; /* link into free list */ + free_entries = p; + num_free_entries++; /* count it as free */ + } + status = PR_ExitMonitor(p->mon); + } else { + status = PR_FAILURE; + } + _PR_UNLOCK_MCACHE(); + + return status; +} + +PR_IMPLEMENT(PRStatus) PR_CWait(void *address, PRIntervalTime ticks) +{ + MonitorCacheEntry **pp; + PRMonitor *mon; + + _PR_LOCK_MCACHE(); + pp = LookupMonitorCacheEntry(address); + mon = pp ? ((*pp)->mon) : NULL; + _PR_UNLOCK_MCACHE(); + + if (mon == NULL) + return PR_FAILURE; + return PR_Wait(mon, ticks); +} + +PR_IMPLEMENT(PRStatus) PR_CNotify(void *address) +{ + MonitorCacheEntry **pp; + PRMonitor *mon; + + _PR_LOCK_MCACHE(); + pp = LookupMonitorCacheEntry(address); + mon = pp ? ((*pp)->mon) : NULL; + _PR_UNLOCK_MCACHE(); + + if (mon == NULL) + return PR_FAILURE; + return PR_Notify(mon); +} + +PR_IMPLEMENT(PRStatus) PR_CNotifyAll(void *address) +{ + MonitorCacheEntry **pp; + PRMonitor *mon; + + _PR_LOCK_MCACHE(); + pp = LookupMonitorCacheEntry(address); + mon = pp ? ((*pp)->mon) : NULL; + _PR_UNLOCK_MCACHE(); + + if (mon == NULL) + return PR_FAILURE; + return PR_NotifyAll(mon); +} + +PR_IMPLEMENT(void) +PR_CSetOnMonitorRecycle(void (*callback)(void *address)) +{ + OnMonitorRecycle = callback; +} |